1. Field of the Invention
The present invention relates to an asynchronous transfer mode ATM system with ring topology, and more particularly, to a protection-switching apparatus and method relative to an ATM cell of the ATM system.
2. Description of the Related Art
Recently, a communication service is upgraded from a voice service, such as a telephone, to a data service, such as Internet, videophone, video on demand (VOD), and so on.
Because the conventional network, such as an integrated service digital network (ISDN) or a leased line, used in the conventional data service allocates a specified frequency to a subscriber forcibly, it is difficult to apply the conventional network to a recent data communication service, such as Internet, requesting an intermittent and a little data flow. Therefore, an asynchronous transfer mode (ATM) system has been requested. One of the ATM systems is a fiber loop carrier-C (FLC-C) system developed by the lead of Korea Telecom (KT).
The FLC-C includes a host digital terminal (HDT) and numerous optical network units (ONUs) with star topology, and performs protection-switching function to an optical fiber line. To be applied to service area and situations, the FLC-C is improved to ring topology and to double star topology. However, up to these days, the HDT and the ONU with ring topology are only used in a communication method of a synchronous digital hierarchy (SDH). Therefore, for the ATM method, not only is an international standard not prepared completely, but also a commercial product does not exist.
The general protection-switching method is described in Korean Patent Application No. 1999-23730 entitled “Protection-Switching Method in Asynchronous Transfer Mode With Ring Topology”, dated on 23 Jun. 1999, by the inventor of this application, in detail.
The conventional FLC-C system with ring topology depends on software program to detect, insert and switch in protection the APS cell entirely. Therefore, the FLC-C system has a problem that the process time is delayed.